The earliest report of an imidazo[4,5-c]quinoline ring system was by Backeberg et al, J. Chem. Soc., 972-977 (1938). However, his report of 4-methyl-1H-imidazo[4,5-c]quinoline and 2,4-dimethyl-1H-imidazo[4,5-c]quinoline (named as 2-methylquin(3:4:5':4')iminazole and 2:2'-dimethylquin(3:4:5':4')iminazole) is known to be erroneous in view of later work of Koenigs and Freund, Chemische Berichte 80, 143 (1947).
A further report by Backeberg, J. Chem. Soc., 1083-1089 (1938) of 2,4-dimethyl-3-phenyl-3H-imidazo[4,5-c]quinoline (named 1'-phenyl-2:2'-dimethylquin(3:4:5':4')iminazole) is also known to be erroneous in view of the above work of Koenigs and Freund.
The first reliable report of a 1H-imidazo[4,5-c]quinoline is by Bachman et al., J. Org. Chem. 15, 1278-1284 (1950) who synthesized 1-(6-methoxy-8-quinolinyl)-2-methyl- 1H-imidazo[4,5-c]quinoline as a possible antimalarial agent.
Surrey et al, J. Am. Chem. Soc. 73, 2413 (1951) synthesized certain 3-nitro- and 3-amino-4-dialkylaminoalkylaminoquinolines as possible antimalarial and antibacterial agents.
Jain et al., J. Med. Chem. 11, pp. 87-92, (1968), synthesized the compound 1-[2-(4-piperidyl)ethyl]-1H-imidazo[4,5-c]quinoline as a possible anticonvulsant and cardiovascular agent.
Baranov et al., Chem. Abs. 85, 94362 (1976), reported several 2-oxoimidazo[4,5-c]quinolines.
Abbasi et al., Monatsh. Chem. 111 (4), pp 963-969 (1980), reported certain 2H-3-hydroxyimidazo[4,5-c]-quinolines.
Berenyi et al, J. Heterocyclic Chem. 18, 1537-1540 (1981), reported certain 2-oxoimidazo[4,5-c]quinolines.
U.S. Pat. No. 3,700,674 (Diehl et al.) describes certain 4-alkylamino-3-nitroquinolines as herbicidal compounds.